Obesity is one of the most significant diseases in modern society and the main factor of obesity is excessive intake of fat. Excessive intake of fat is known to cause not only obesity but also diabetes, hyperlipidemia, hypertension, arteriosclerosis, and the like that are attributable to obesity. The condition in which two or more of hyperglycemia, hypertension, and hyperlipidemia develop with visceral fat obesity is called metabolic syndrome (visceral fat syndrome), which is at high risk of causing cardiac diseases and stroke and thus has been regarded as a problem in recent years. As a therapeutic agent for obesity, for example, Xenical®, which has a suppressive action on fat absorption from the gastrointestinal tract due to its lipase inhibitory activity, is commercially available as an anti-obesity agent; however, its side effects such as steatorrhea, increased frequency of defecation, loose stool, diarrhea, and stomachache have been reported and the agent thus cannot be necessarily safe (Non-Patent Document 1).
In order to prevent obesity, cutting calories on a restrictive diet is an effective way. Nevertheless, it is often hard to practice it in daily life because substantial nutritional guidance has to be received. Accordingly, suppressing in a safe and healthy manner the absorption of diet-derived fat into the body is expected to be a realistic and effective measure for treatment of obesity and obesity-related diseases or health enhancement.
Under these circumstances, the development of specified health foods that are safe and proven effective in humans is attracting attention. To date, the following food materials which suppress the elevation of serum triglyceride level after meals are commercially marketed as specified health foods: globin digest which suppresses fat absorption by its pancreatic lipase inhibition; diacylglycerol, which has digestive and absorptive properties different from triacylglycerol; eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are purified from fish oil; and the like.
Also, recent interest is focusing on plant-derived lipase inhibiting active substances, and particularly, the following polyphenols which have lipase inhibitory activity have been reported: plant bark-derived tannin; tannins and flavonoids and glycosides thereof in the legume Cassia nomame; lipid absorption-inhibiting foods containing epigallocatechin gallate and epicatechin gallate, which are main components in green tea; lipase inhibitors comprising water extracts from pepper, shimeji mushroom, pumpkin, maitake mushroom, seaweed Hizikia fusiformis, green tea, oolong tea, and the like; flavones and flavonols; hydroxybenzoic acids (gallic acid), triterpene compounds and derivatives thereof; anti-obesity agents containing, as an active ingredient, procyanidin from tamarind; and the like. Further known are lipase inhibitory action of grape seed extract (Non-Patent Document 2); lipase inhibitory action from Salacia reticulate-derived polyphenol, and anti-obesity action in rats (Non-Patent Document 3); oolong tea extract-derived anti-obesity action in mice (Non-Patent Document 4); and the like. In addition, teas contain a lot of catechins, many components of which have been separated and identified (Non-Patent Document 5), and there are reports on lipase inhibitors containing tea-derived components (Patent Documents 1 and 2). Above all, theaflavins, known as pigments of black tea and oolong tea, exhibit strong lipase inhibitory activity in proportion to the number of gallate groups in a molecule (Patent Document 2, Non-Patent Document 6). However, the content and proportion of these theaflavins are not constant among teas.
Alfa-glucosidase inhibiting substances have an inhibitory action on the elevation of blood glucose level by inhibiting alfa-glucosidase, which is localized on small intestinal epithelium, and by suppressing or delaying the decomposition and absorption of sugar. Accordingly, alfa-glucosidase-inhibiting substances are useful in various diseases such as diabetes and obesity, which are derived from the chronicity of high blood sugar symptoms.
Since alfa-glucosidase inhibitory activity was discovered in malt component in 1933, many alfa-glucosidase-inhibiting substances that are derived from wheat and pulse have been discovered. In 1966, nojirimycin, which has alfa-glucosidase inhibitory activity, was isolated from a microbial metabolite and its structure was determined. From mulberry leaf extract, a related compound of nojirimycin, 1-deoxynojirimycin, was obtained, which is known to have alfa-glucosidase inhibitory activity, and a method of extraction for keeping the activity from decreasing is disclosed (Patent Document 3).
A compound that contains a 13-membered ring cyclitol structure having a sulfoxide, which is isolated from the extract of the root of Salacia reticulate, is reported to have maltase inhibitory activity (Patent Document 4). Diacylated pelargonidin, cyanidin, and peonidin 3-sophoroside-5-glucosides are reported to have maltase inhibitory activity as an anthocyanin compound isolated from morning glories or the root of purple sweet potato (Non-Patent Document 7). The maltase inhibitory activity has also been confirmed in the components contained in tea leaves, such as theasinensin A, theaflavin derivatives having a galloyl group, and proanthocyanidins having epiafzelechingallate as a constitutional unit. Although theaflavin derivatives having a galloyl group have maltase inhibitory activity, they are contained in tea leaves in only a small proportion, 0.1 to 0.2% (Patent Document 5, Non-Patent Document 8).
Black tea theaflavins and green tea catechins are reported to have alfa-glucosidase inhibitory activity (Non-Patent Document 8); the activity has been confirmed in catechins having a galloyl group at their 3 position including epigallocatechin-3-O-gallate (hereinafter referred to as “EGCG”) and epicatechin-3-O-gallate, and theaflavins including theaflavin-3-O-gallate and theaflavin-3,3′-di-O-gallate. The fractions and the like of black tea have also been examined for their alfa-glucosidase inhibitory activity; polymeric fractions formed by fermentation are also known to have the activity (Non-Patent Document 9).
On the other hand, it is known that in fermentation process in production of black tea or oolong tea, polyphenols such as catechins or gallic acid are condensed into a compound having a benzotropolone ring through the activity of enzymes such as polyphenol oxidase in tea leaves (Non-Patent Document 10).
It is reported that aside from theaflavins, many benzotropolone ring-containing compounds are present in teas. Reported are, for example, apoptosis induction caused by purpurogallin derivatives (Patent Document 6) and a method of manufacturing epitheaflagallins for use in foods (Patent Document 7), an enzymatic method of manufacturing a theaflavin type trimer, theadibenzotropolone A, and presence thereof in black tea (Non-Patent Document 11), and the like. The anti-inflammatory actions of various benzotropolone ring-containing compounds (Non-Patent Document 12) are also known. Nevertheless, for benzotropolone ring-containing compounds other than theaflavins and epitheaflagallins, nothing is known about their lipase inhibitory action relating to fat absorption and their alfa-glucosidase inhibitory action relating to their inhibitory action on the elevation of blood glucose level.